2231c. For ornamental purposes, besides coloured glass, glass may have a ground surface, which is obtained by grinding it with a stone, or by the use of fluoric acid. Embossed glass, which permits the application of devices, according to the fancy of the designer or intention of the manufacturer, is effected by covering the square of glass with a varnish, except where the device is intended. An acid is then poured on which eats away the uncovered glass for a small depth. The varnish is then cleaned off, and the general surface is ground as usual. Its imitation is obtained by covering the plate with a varnish, a lace or stencil pattern placed on it, then dusted over with a colouring matter in the state of fine powder, and the plate thus treated sufficiently heated to vitrify and fix the dusted varnish to the glass. Messrs. Chance, and other manufacturers, sell various enamelled stencilled patterns, as white enamelled, enamelled and flocked, embossed repeated pattern, stained enamelled, and double etched glass, self shadowed glass, patent polychromatic glass, printed glass, stamped in colours, and many other kinds, all which are better seen at the factories than described. 2231d. The compressive strength of glass, that is, its resistance to a force tending to crush it, is about 12 tons per square inch. This is nearly equal to one quarter the strength of cast iron. Glass has three times the specific gravity of iron. In the form of bars, a favourable shape for developing a highly tensile strength, one ton per square inch of area is the highest amount to be assumed for it. 2231e. MOSAIC WORK. This durable manner of decoration in glass, requires a short notice. The Roman mosaic is composed of pieces of enamelled glass, thus rendered opaque, sometimes called smalto and sometimes paste, made of all kinds of colours and of every different hue. For large pictures they take the form of small cakes. For small works they are produced as threads, varying in thickness from that of a piece of string to the finest cotton thread. The Venetian mosaic pictures are formed of pieces of very irregular shapes and sizes, of all colours and tones of colours; the ground tint almost invariably prevailing is gold. The manner of execution is always large and coarse, and rarely approaches any neatness of joint or regularity of bedding. Opus Grecanicum consists in the insertion, into grooves cut in white marble to a depth of about half an inch, of small cubes of these coloured and gilded smulto, and in the arrangement of these forms in such geometrical combination as to compose the most elaborate patterns. It was customary to combine the bands of this mosaic work with large slabs of Serpentine, Porphyry, Pavonazzetto, and other valuable marbles, and to use it in the decoration of ambones, cancelli, &c.; its use externally was comparatively rare. The hexagon, triangle, square, and octagon, form the usual bases of most of the specimens of this ingenious art to be found in Italy. Patterns of accumulating intricacy are seen at Palermo, and at Monreale. Illustrations in colour are given in the useful work on Mosaics, by M. D. Wyatt. 2231f. Coloured enamels are made of a vitreous paste (or glass), to this are added other mineral substances, which, when properly prepared and fused together, impart to the paste its density and extreme hardness, and also its colour; the better the manufacture, the more satisfactory the appearance and the greater the durability of the mosaic work. In an imperfect manufacture, the mosaic is liable to be injured by damp, smoke, and all atmospheric changes; when well produced, they can be made to give precisely the same effect as the painting. 2231g. Gold and silver enamels were introduced: these are made of the precious metals, but in such thin sheets that their use is comparatively inexpensive. The process is a difficult one, for, to produce true gold and silver enamels, great knowledge and experience are necessary. On a ground of thick glass or enamel, according as it is desired to render the gold enamel transparent or opaque, or to impart to it a warm or variegated colour, there is laid a leaf of gold or silver, which is attached principally by the action of fire; then a film of the purest glass is spread over it, and this may either be perfectly colourless or of any tint that may be required. When well manufactured, these thin layers, after being fused, become perfectly united with each other, and form a homogeneous body, and the metal is for ever protected against all possibility of injury from any cause except actual violence. 2231h. Stevens has produced a new kind of glass mosaic, executed at about one third the price of the ancient manufacture of this kind. The glass is stained or gilt, and the method is adapted for many purposes. Messrs. Rust are working in gold, silver, and enamel mosaics of their own invention; and Dr. Salviati employs his indestructible system of Venetian enamel-mosaic, in works, in a comparatively inexpensive and expeditious manner. At the Wolsey tomb-house, at Windsor, the entire ceiling, consisting of 2,100 feet, was decorated in the space of ten months, including the time of the transit of the mosaics from Venice; and was executed, with the scaffolding, at the price of 4,7251. It was also employed at St. Paul's Cathedral, for the figure of the prophet Isaiah, covering 250 feet, which was executed and fixed in two months, at the price of 6007. (Lecture read at Leeds, by A. Salviati, 1865.) 2231. The cements used are of three sorts. The first, for large tesseræ in forming floors, is composed of pitch, mixed with a black carth. The second, for stones of a mid dling dimension, is made of tufa and oil. The third, for the more delicate mosaics of pieces of glass, is made of white of lime, pounded bricks, gum andragan, and the white of eggs. The ancients are said to have used 1 part of slaked lime and 3 parts of pounded marble, made up with water and white of egg. But as this is considered to harden too quickly, a mixture of 1 part of slaked lime, and 3 parts of powdered travertine stone, mixed up with linseed oil, and kept stirred every day, is used, adding oil as it dries. The mass is ready sooner in warm weather than in cold, varying from 20 to 30 days, when it is like a smooth ointment. For the larger works, Keene's, Portland, or other similar cements might be used. SECT. IX. 2232. In the finishing of our dwellings, the decoration owes much of its effect to the labours of the plasterer: it is in his department to lay the ceilings, and to give, by means of plaster, a smooth coat to the walls, so as to hide the irregularities left by the bricklayer and mason, and make them sightly and agreeable. He also, in the better sort of buildings, furnishes plain and decorated mouldings for the cornices and ceilings; and in the external parts, where stone is expensive or not to be procured, covers the exterior walls with stucco or other composition imitative of stone. 2233. The plasterer's tools are-a spade or shovel of the usual description; a rake with two or three prongs bent downwards from the line of the handle, for mixing the hair and mortar together; stopping and picking out tools; rules called straight edges; wood models; and trowels of two sorts and various sizes, namely, the laying and smoothing tools, consisting of flat pieces of hardened iron, about 10 inches long, and 2 inches wide, very thin, and ground to a semicircular shape at one end, but square at the other. Near the square end on the back of the plate a small iron rod is rivetted, with two legs, whereof one is fixed to the plate, and a round wooden handle is adapted to the other. All the first coats of plastering are laid on with this tool, as is also the last, or setting, as it is technically called. The other sorts of trowels are of three or more sizes, and are used for gauging the fine stuff and plaster for cornices, mouldings, &c. The length of these trowels is, the largest about 7 inches in length on the plate, and the smallest 2 or 3 inches: they are of polished steel, converging gradually to a point, with handles of mahogany adapted to the heel or broad end with a deep brass ferrule. 2234. The stopping and picking out tools are of polished steel, of various sizes, about 7 or 8 inches long and half an inch broad, flattened at both ends, and somewhat rounded, They are used for modelling and finishing mitres and returns to cornices, as also for filling up and finishing ornaments at their joinings. There is also used a small instrument, which is a piece of thin fir 6 or 7 inches square, called a hawk, with a handle vertical to it, for holding small quantities of plaster. 2235. The composition used by the plasterer is a groundwork of lime and hair, on which, for the finish, a coating of finer material is laid. The sorts of it are various; as, for instance, white lime and hair mortar on bare walls; the same on laths as for partitions and plain ceilings; for renewing the insides of walls; roughcasting on laths; plastering on brickwork with finishing mortar, in imitation of stone work, and the like upon laths. For cornices and the decorations of mouldings, the material is plaster of Paris, one which facilitates the giving by casts the required form and finish to the superior parts of his work. The plasterer uses it also for mixing with lime and hair, where the work is required to dry and set hard in a short time. For inside work, the lime and hair, or coarse stuff, is prepared, like common mortar, with sand; but in the mixing, hair of the bullock, obtained from the tanners' yards, is added to it, and worked in with the rake, so as to distribute it over the mass as equally as possible. 2236. What is called fine stuff is made of pure lime, slaked with a small quantity of water, and afterwards, without the addition of any other material, saturated with water, and in a semi-fluid state placed in a tub to remain until the water has evaporated. In some cases, for better binding the work, a small quantity of hair is worked into the composition. For interior work, the fine stuff is mixed with one part of very fine washed sand to three parts of fine stuff, and is then used for trowelled or bastard stucco, which makes a proper surface for receiving painting. 2237. What is called gauge stuff is composed of fine stuff and plaster of Paris, in proportions according to the rapidity with which the work is wanted to be finished. About four-fifths of fine stuff to one of the last is sufficient, if time can be allowed for the setting. This composition is chiefly used for cornices and mouldings, run with a wooden mould. We may here mention that it is of the utmost importance, in plasterers' work, that the lime should be most thoroughly slaked, or the consequence will be blisters thrown out upon the work after it is finished. Many plasterers keep their stuffs a considerable period before they are wanted to be used in the building, by which the chance of blistering is much lessened. 2238. When a wall is to be plastered, it is called rendering; in other cases the first operation, as in ceilings, partitions, &c., is lathing, nailing the laths to the joists, quarters, or battens. If the laths are oaken, wrought iron nails must be used for nailing them, but cast iron nails may be employed if the laths are of fir. The lath is made in three and four foot lengths, and, according to its thickness, is called single, something less than a quarter of an inch thick, lath and half, or double. The first is the thinnest and cheapest, the second is about one-third thicker than the single lath, and the double lath is twice the thickness. When the plasterer laths ceilings, both lengths of laths should be used, by which in nailing, he will have the opportunity of breaking the joints, which will not only help in improving the general key, (or plastering insinuated behind the lath, which spreads there beyond the distance that the laths are apart,) but will strengthen the ceiling generally. The thinnest laths may be used in partitions, because in a vertical position the strain of the plaster upon them is not so great; but for ceilings the strongest laths should be employed. In lathing, the ends of the laths should not be lapped upon each other where they terminate upon a quarter or batten, which is often done to save a row of nails and the trouble of cutting them, for such a practice leaves only a quarter of an inch for the thickness of the plaster; and if the laths are very crooked, which is frequently the case. sufficient space will not be left to straighten the plaster. (2246b.) 2239. After lathing, the next operation is laying, more commonly called plastering. It is the first coat on laths, when the plaster has two coats or set work, and is not scratched with the scratcher, but the surface is roughed by sweeping it with a broom. On brickwork it is also the first coat, and is called rendering. The mere laying or rendering is the most economical sort of plastering, and does for inferior rooms or cottages. 2240. What is called pricking up is the first coat of three-coat work upon laths. The material used for it is coarse stuff, being only the preparation for a more perfect kind of work. After the coat is laid on, it is scored in diagonal directions with a scratcher (the end of a lath), to give it a key or tie for the coat that is to follow it. 2241. Lath layed or plastered and set is only two-coat work, as mentioned under laying, the setting being the guage or mixture of putty and plaster, or, in common work, of fine stuff, with which, when very dry, a little sand is used; and here it may be as well to mention, that setting may be either a second coat upon laying or rendering, or a third coat upon floating, which will be hereafter described. The term finishing is applied to the third coat when of stucco, but setting for paper. The setting is spread with the smoothing trowel, which the workman uses with his right hand, while in his left he uses a large flat-formed brush of hog's bristles. As he lays on the putty or set with the trowel, he draws the brush, full of water, backwards and forwards over its surface, thus producing a tolerably fair face for the work. 2242. Work which consists of three coats is called floated: it takes its name from an Instrument called a float, which is an implement or rule moved in every direction on the plaster while it is soft, for giving a perfectly plane surface to the second coat of work. Floats are of three sorts: the hand float, which is a short rule, that a man by himself may use; the quirk float, which is used on or in angles; and the Derby, which is of such a length as to require two men to use it. Previous to floating, which is, in fact, the operation of making the surface of the work a perfect plane, such surface is subdivided in several bays, which are formed by vertical styles of plastering, (three, four, five, or even ten feet apart,) formed with great accuracy by means of the plumb rule, all in the same plane. These styles are called screeds, and being carefully set out to the coat that is applied between them, the plaster or floating laid on between them is brought to the proper surface by working the float up and down on the screeds, so as to bring the surface all to the same plane, which operation is termed filling out, and is applicable as well to ceilings as to walls. This branch of plastering requires the best sort of workmen, and great care in the execution. 2243. Bastard stucco is of three coats, the first whereof is roughing in or rendering, the second is floating, as in trowelled stucco, which will be next described; but the finishing coat contains a small quantity of hair or white sand. This work is not hand floated, and the trowelling is done with less labour than what is denominated trowelled stucco. 2244. Trowelled stucco, which is the best sort of plastering for the reception of paint, is formed on a floated coat of work, and such floating should be as dry as possible before the stucco is applied. In the last process, the plasterer uses the hand float, which is made of a piece of half-inch deal, about nine inches long and three inches wide, planed smooth, with its lower edges a little rounded off, and having a handle on the upper surface. The ground to be stuccoed being made as smooth as possible, the stucco is spread upon it to the extent of four or five feet square, and, moistening it continually with a brush as he proceeds, the workman trowels its surface with the float, alternately sprinkling and rubbing the face of the stucco, till the whole is reduced to a fine even surface. Thus, by small portions at a time, he proceeds till the whole is completed. The water applied to it has the effect of hardening the face of the stucco, which, when finished, becomes as smooth as glass. 2245. From what has been said, the reader will perceive that mere laying or plastering on laths, or rendering on walls, is the most common kind of work, and consists of one coat only; that adding to this a setting coat, it is brought to a better surface, and is two-coat work; and that three-coat work undergoes the intermediate process of floating, between the rendering or pricking up and the setting. 2245a. This plain plastered surface has received an improvement in a method of stamping or incising it, while wet, the invention, in 1857, of Mr. Benj. Ferrey, architect. "It is well known that the external rough-casting on old timber houses was stamped or wrought in small devices, known by the term pargetting; but it never assumed the importance of extensive wall decorations. The plan now proposed is to impress the common stucco with geometrical or other forms, and applied according to taste, either under string courses, around arches, in spandrils, soffites, or in large masses of diapering; and texts may be imprinted on the plaster instead of being simply painted on the walls. If colour be desired, it can be effected by mixing the desired colour with the coat forming the groundwork, then by laying the stencilled pattern against it, and filling in the solid portions of the device with the ordinary stucco or plaster." The process does not pretend to do more than enliven wall surfaces, but for this purpose it is very effective. Whippingham Church, in the Isle of Wight, is decorated in this manner, with devices in different colours. 2246. Ceilings are set in two different ways; the best work is where the setting coat is composed of plaster and lime putty, commonly called gauge stuff (2237). Common ceilings are formed with plaster without hair, as in the finishing coat for walls set for paper. The deflection of th of an inch for each foot in length is not injurious to ceilings; indeed, the usual allowance for settlement is about twice that quantity. Ceilings have been found to settle about four times as much without causing cracks, and have been raised back again without injury. (Barlow, p. 179.) 2246a. In Dublin, the designations in plasterers' work are different to those we have named above. Work to ceilings is described as "Lath scratched, floated, and coated;" while to walls it is described as “scratched, floated, and coated." Skimming, to plasterers work, is a very thin coat of white (i.e. lime) put on float work to smoothen it, and to leave a clean face; coated is the term for better work of the same character. 22466. Hitchin's fireproof plaster appeared about 1877; it is valued for its simplicity, economy, and facility in working. The fibrous slab plastering is always dry and ready for fixing. The slabs on a wire base protect ceilings, walls, and woodwork from fire. Casings on wire base protect iron and wood girders, columns and such like. Pugging slabs are used for prevention of sound. Wilkinson and Co's fibrous plaster slabs are intended for lining walls and ceilings, and for fixing under slating; also to partitions and under floor-boards for deadening sound. 2246c. Johnson's patent rolled fireproof wire lathing is now occasionally used as a substitute for wood laths. It is a foundation for fire-resisting plaster. His woven wire and iron fireproof partition wall is intended to supersede the ordinary stud and brick partitions, and is applicable to roofs. Metal laths, of thin sheet iron, by Edwards's patent, are for use in fire-resisting ceilings, partitions, and doors. Wirework, in place of lathing, for forming ceilings and other plaster surfaces, patented in 1841 by L. Leconte, had been previously adopted in the building of the Pantechnicon, near Belgrave Square. 2246d. Nickson and Waddingham have patented a slate ground for plaster, by using, instead of laths, those slates which do not turn out in the quarries sufficiently wide for sized roofing slates; an immense number of them being necessarily thrown aside daily, although of the best quality. The slates are fixed in. apart; the plaster to be in. thick, of well haired stuff, which keys itself between the slates; they run from 12 to 7 in. long and upwards. The system was worked about 1862 at Manchester. 2247. Pugging is plaster laid on boards, fitted in between the joists of a floor to prevent the passage of sound between two stories, and is executed with a coarse stuff made of lime and hay chopped into lengths of about 2 inches. Silicate cotton or slag wool, nailed in slabs to the under side of the joists of a floor, or against the studs of a partition, acts as a nonconductor of heat or cold; it is also fireproof, sound-proof, vermin-proof, and frost-proof. One ton of it, one inch thick, covers 1,800 square feet. This material is now greatly used; also for protecting exposed iron work. Asbestos millboard is another material greatly employed for lining partitions, to deaden sound passing through; as well as for fireproof purposes. 2248. The following materials are required for 100 yards of render set; viz. 1 hundred of lime, 1 double load of river sand, and 4 bushels of hair; for the labour, 1 plasterer 3 days, 1 labourer 3 days, 1 boy 3 days; and upon this, 20 per cent. profit is usually allowed, For 130 yards of lath plaster and set-1 load of laths, 10,000 nails, 2 hundred of lime, 1 double load of river sand, 7 bushels of hair; for the labour, 1 plasterer 6 days, 1 labourer 6 days, 1 boy 6 days; and upon this, as before, 20 per cent. is usually allowed. 1 bushel of Portland or Roman cement will cover, yards super. 1 ditto, and 1 of sand inch 21 1 ditto, and 2 ditto 1 ditto, and 3 ditto 1 cwt. of mastic and 1 gallon of oil 6 in. 2's 1 cubic yard of chalk lime, 2 yards of sand, and 3 bushels of hair, will cover 75 yards of render set on brickwork; 70 yards on lath; or 65 yards plaster; or render two coats and set on brick; and 60 yards on lath. Floated work requires about the same as two coats and set. A bundle of laths and 500 nails will cover about 4 yards superficial. Two hundred laths, 4 feet long, are required for a square. A bundle of laths contains 500 feet nominally. 2249. In the country, for the exterior coating of dwellings and outbuildings, a species of plastering is used called roughcast. It is cheaper than stucco or Roman cement, and therefore suitable to such purposes. In the process of executing it, the wall is first pricked up with a coat of lime and hair, on which, when tolerably well set, a second coat is laid on of the same materials as the first, but as smooth as possible. As fast as the workman finishes this surface, another follows him with a pailful of the roughcast, with which he bespatters the new plastering, so that the whole dries together. The roughcast is a composition of small gravel, finely washed, to free it from all earthy particles, and mixed with pure lime and water in a state of semi-fluid consistency. It is thrown from the pail upon the wall, with a wooden float, about 5 or 6 inches long, and as many wide, formed of half-inch deal, and fitted with a round deal handle. With this tool, while the plasterer throws on the roughcast with his right hand, in his left he holds a common whitewasher's brush dipped in the roughcast, with which he brushes and colours the mortar and the roughcast already spread, to give them, when finished, an uniform colour and appearance. 2249a. Gypsum or plaster of Paris is largely used in France for the construction of walls, both internally and externally, as well as for rendering them afterwards. We adopt This the following method of working it, as explained by G. R. Burnell: "The coarser kinds of plaster are used for rendering; the finer qualities for ceilings, cornices, and decorative works. For walls, the plaster must be gauged stiff for the first coats, and more fluid for the setting coat. For cornices worked out in the solid, the core is made of stiffly gauged plaster, which is floated with finer material, and lastly finished off with plaster laid on by hand, about the consistence of cream. Practice only can ascertain the precise degree of stiffness to be given, as every burning yields a different quality of plaster. When walls are to be rendered, they require to be first jointed, and then wetted with a broom. The surface is then covered with a coat of thinly gauged stuff, laid on with a broom, or at least worked with a trowel in such a manner as to leave sufficient hold for the next coat. is gauged stiff, and is laid on with a trowel; it is floated with a rule, but the face is finished with a hand trowel; the surfaces, however, are never so even, or the angles so square and true, as in the usual plasterers' work adopted in England. The ceilings are lathed about 3 to 3 inches from centre to centre, and the plaster poured in from above on to a sort of flat centering, leaving about an inch for the thickness of plaster; the ceiling coat is added after the centering is removed. The better descriptions are made with laths 4 inches from centre to centre, the space between ceiling and floor filled up with light work, and the under and upper surfaces rendered to receive the ceiling and tiles." 22496. With gypsum, only about ths of the evaporation arises as from ordinary plastering. A series of experiments made in 1850, proved that the cost of ordinary works need not exceed in any sensible proportion, if at all, those usually called "render set; " and that they are strictly the same as "render float and set." A room was begun and finished in thirty hours, whilst a common lime and hair rendering coat would have required, properly speaking, about a month. French plaster must never be used in any position where moisture is likely to affect it for any length of time. It is very hygrometric, and soon decays if kept moist. If it be used as mortar, as in brick-nogged partitions, to be covered over immediately, a space for its expansion must be allowed. In France, a small space is left between the wall and partitions; this is filled in by the plastering coat. The same observation applies to floors with plaster pugging, and even to cornices with a large body of that material, the mitres and returns being executed some time after the straight mouldings. 2250. In forming the coves and cornices which are applied below the ceilings of rooms, it is of the greatest importance to make them as light as possible, for the plaster whereof they are formed is heavy, and ought not to depend merely on its adhesion to the vertical and horizontal surfaces to which it is attached. Hence, when cornices run of large dimen |